Immunological Identification of a Common Precursor to Arginine
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Proc. Natl Acad. Sci. USA Vol. 78, No. 2, pp. 766-769, February 1981 Biochemistry Immunological identification of a common precursor to arginine vasopressin and neurophysin II synthesized by in vitro translation of bovine hypothalamic mRNA (signal sequence/polyprotein/processing/core glycosylation/tunicamycin) HARTWIG SCHMALE AND DIETMAR RICHTER* Institut ffir Physiologische Chemie, Abteilung Zellbiochemie, Universitit Hamburg, Martinistrasse 52, 2 Hamburg 20, Federal Republic of Germany Communicated by Nathan 0. Kaplan, October 17, 1980 ABSTRACT mRNA from membrane-bound polysomes of bo- MATERIALS AND METHODS vine hypothalamus was translated in an mRNA-dependent cell- free system from reticulocyte lysate or wheat germ. The trans- Bovine neurophysin I (Np I) and neurophysin II (Np II) and lation products were identified by immunoprecipitation with an- rabbit antisera to Np I and Np II were purchased from Bio- tibodies to either neurophysin H or arginine vasopressin followed products (Brussels); according to the supplier the antisera by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. An against Np II were passed over a Np I-Sepharose column to im- immunoreactive polypeptide was obtained with an apparent Mr prove the specificity of anti-Np II. The same was done for anti- of 21,000. Sequential immunoprecipitation studies indicated that the Mr 21,000 product is a common precursor to neurophysin II Np I. The supplier claimed that this procedure reduced cross- and arginine vasopressin. The specificity of the immunoprecipi- reactivity of the neurophysin antisera to less than 0.5% as tation was demonstrated by competition with excess amounts of judged by radioimmunoassay. Both these and the rabbit anti- unlabeled neurophysin H or arginine vasopressin; little or no com- serum against AVP (Ferring, Kiel) were precipitated with 28 petition was observed with unlabeled neurophysin I or oxytocin. g of ammonium sulfate per 100 ml. According to Ferring, there Processing experiments with microsomal membranes from dog is no crossreaction between anti-AVP and oxytocin or lysine pancreas or tunicamycin-treated ascites tumor cells showed that the Mr 21,000 polypeptide is the prepro form. It was converted vasopressin and less than 30%o with vasotocin; anti-AVP does not to a pro form with Mr 19,000 suggesting a pre sequence of ap- discriminate between oxidized and reduced AVP. Hypothalamic proximately 15 amino acids. The Mr 19,000 polypeptide was core- mRNA was isolated as reported (13). The cell-free wheat germ glycosylated to an apparent Mr of 23,000, indicating that the neu- system was prepared according to published procedures (13). rophysin II-arginine vasopressin precursor is a glycopolypeptide. The reticulocyte lysate assay system came from New England Nuclear. EDTA-stripped microsomal membrane fractions from Oligopeptides such as the bacterial antibiotics gramicidin and dog pancreas (14) were kindly provided by B. Dobberstein tyrocidin are synthesized in a nonribosomal fashion on polyen- (Heidelberg). Microsomal membranes from ascites tumor cells zyme templates (1, 2). Reports that oligopeptides of hypothal- (15, 16) treated with tunicamycin (Lilly) and immobilized mem- amus from mammals also might be synthesized by a nonribo- branes from Staphylococcus aureus (17) were prepared as somal mechanism are still controversial (3-5). In vitro biosyn- reported. thesis of the hypothalamic nonapeptide hormones vasopressin and oxytocin has not yet been resolved. Although Sachs (6) sug- gested more than a decade ago that vasopressin may be syn- RESULTS thesized by a ribosome-dependent mechanism via a precursor Identification of the Immunoreactive Products. mRNA iso- polypeptide, only recently a tentative glycopolypeptide pre- lated from detached polysomes of bovine hypothalami was cursor with an apparent M, of 20,000 has been isolated from the translated in a cell-free system from reticulocyte lysate or wheat hypothalamus of rats and mice (7-9). This precursor gave rise germ in the presence of [3S]cysteine. Purified antibodies to a vasopressin-like peptide after trypsinization (7). In addition raised against neurophysin II (anti-Np II) or arginine vasopres- the precursor crossreacted with antibodies raised against one sin (anti-AVP) were used to identify the translation products. of the hypothalamic cysteine-rich neurophysins (8, 9) which is The immunoreactive products precipitated with S. aureus im- known to transport vasopressin to its storage site in the posterior munoabsorbant were analyzed by sodium dodecyl sulfate/ pituitary (10). polyacrylamide gel electrophoresis. With anti-Np II, two prod- If the precursor hypothesis is valid it should be possible to ucts with apparent Mr of 21,000 and 18,000 were obtained, demonstrate biosynthesis of a vasopressin-neurophysin pre- whereas with anti-AVP only the Mr 21,000 product was found cursor directly by translation of hypothalamic mRNA in cell- (Fig. 1, lanes 1 and 2). The Mr 18,000 product was barely de- free systems. Although a number of groups have reported the tectable when mRNA was translated in the cell-free wheat germ synthesis of neurophysin precursors in cell-free systems (11-13), system. At present it is not possible to decide whether the Mr identification of vasopressin-like sequences within the reported 18,000 product represents another discrete neurophysin II-like precursors has been lacking. The present communication re- polypeptide (18) or whether it is a premature Mr 21,000 poly- ports mRNA-directed synthesis of a common precursor to ar- peptide derived from a pre-termination event. ginine vasopressin (AVP) and neurophysin II and its processing The specificity of the immune reactions was demonstrated and core glycosylation; specific antibodies were used for identification. Abbreviations: Np I, bovine neurophysin I; anti-Np I, antibodies against Np I raised in rabbits; Np II, bovine neurophysin II; anti-Np II, anti- The publication costs of this article were defrayed in part by page charge bodies against Np II raised in rabbits; AVP, arginine vasopressin; anti- payment. This article must therefore be hereby marked "advertise- AVP, antibodies raised against AVP in rabbits. nent" in accordance with 18 U. S. C. §1734 solely to indicate this fact. * To whom reprint requests should be addressed. 766 Downloaded by guest on October 2, 2021 Biochemistry: Schmale and Richter Proc. Natl. Acad. Sci. USA 78 (1981) 767 Anti-Np II: + _- - + - Anti-Np I: Anti-AVP: + - ± + + ± + _- Competing peptides cr > W" 0. > U) z C a z . a - Mr. x 10 s x 103 c 21 21 18 18 __ .:... o - 16.5 1 2 3 4 5 6 7 8 9 10 11 FIG. 1. Gel electrophoresis of the Np ll-AVP precursor after synthesis and immunoprecipitation. Bovine hypothalamic mRNA (0.5 Mug) prepared from detached polysomes and purified by oligo(dT)-cellulose chromatography (13) was translated in the wheat germ system (lanes 3 and 4) or the reticulocyte lysate system (remaining lanes) in a total volume of 25 Ml [10 ,l of lysate, 2 ,1 of translation cocktail, 0.5 Ml of 32.5 mM Mg(OAc)2, 2 ,l of 1 M KOAc, and 20 MCi of [35S]cysteine]. After incubation at 370C the mixture was diluted with 3 vol of cold 10 mM Na phosphate, pH 7.6/ 1 mM EDTA/1% Triton X-100 containing 200 units of Antagosan (Behring, Marburg) per ml. For immunoprecipitation, 10 Mug of anti-Np I or anti- Np II IgG or 20 Mg of anti-AVP IgG (1.4 A280 units = 1 mg) were added and incubated at 40C for 20 hr. Nonspecific aggregates were removed by centrifugation at 15,000 x g for 15 min; the supernatant fraction was subjected to indirect immunoprecipitation with S. aureus immunoabsorbant (13, 17). After washing by three cycles of centifugation (8000 x g, 2 min) and resuspension in 20 mM Tris'HCl, pH 7.6/1 mM EDTA/500 mM NaCl/ 0.5% Triton X-100, the antigen-antibody complexes were dissociated from the staphylococci by boiling for 3 min in 62.5 mM Tris-HCl, pH 6.8/5% (wt/vol) sodium dodecyl sulfate/10% (wt/vol) glycerol/4% (vol/vol) 2-mercaptoethanol and subsequently subjected to sodium dodecyl sulfate/15% polyacrylamide gel electrophoresis. The dried slab gels were fluorographed. [For the total translation products (prior immunoprecipitation), see ref. 13.] In this and the following fluorogram, lanes were derived from different gels and aligned according to the position of marker proteins (a, oval- bumin, Mr 43,000; b, carbonic anhydrase, 30,000; c, soy bean trypsin inhibitor, 20,000; d, a-lactalbumin, 14,400). Where indicated, the immuno- precipitation was carried out in the presence of excess (10 Mg per assay) of unlabeled competing peptide [bovine serum albumin (BSA), AVP, Np II, oxytocin (OT), or luteinizing hormone-release hormone (LHRH)]. by competition experiments. Excess AVP effectively inhibited munoprecipitation step, implying that the Mr 21,000 polypep- binding of the Mr 21,000 product to AVP specific antibodies tide is a common precursor to Np II and AVP. In some exper- (Fig. 1, lane 5); no inhibition was observed with excess Np II Table 1. Sequential immunoprecipitation of the (lane 6), oxytocin or LHRH On the (lane 7), (lane 8). other hand Np II-AVP precursor excess Np II (lane 9) but not AVP (lane 10) inhibited binding of the Mr 21,000 and 18,000 polypeptides to anti-Np II. Np I Total cpm in Np ll-AVP was significantly less potent as a competitor than Np II although Antibodies added precursor at high concentrations Np I was also inhibitory (not shown). 1st step 2nd step 1st step 2nd step II did not Apparently, anti-Np discriminate completely be- Anti-Np II Anti-AVP 1192 192 tween two reverse the neurophysins. Similarly, in the experi- Anti-AVP 1044 290 ment anti-Np I crossreacted with the Mr 21,000 and 18,000 Anti-Np II precursors, although it predominantly reacted with a polypep- Translation in the reticulocyte lysate system, immunoprecipitation, tide of Mr 16,500 (lane 11).